Carburetors are well known devices for mixing gasoline and air together and for supplying this fuel/air mixture to the combustion chambers of an internal combustion engine. Often, the carburetor is used on the engine powering a motor vehicle, such as an automobile or motorcycle, though carburetors are used on non-vehicular internal combustion engines as well. One traditional carburetor is known as the "butterfly" type. This name comes from the shape of the pivotal throttle plate or throttle valve located inside the carburetor body which somewhat resembles a butterfly. Thus, the throttle plate is also sometimes referred to as the butterfly valve.
A butterfly carburetor includes a carburetor body which is secured to the intake manifold of the engine. The carburetor body includes an airflow passage in which incoming atmospheric air is mixed with fuel prior to being admitted to the intake manifold. The throttle plate is located within and generally at the end of the airflow passage which is closest to the intake manifold. A venturi section in the airflow passage is located upstream of the throttle plate. A first fuel jet is located in or adjacent the venturi section so that air passing through the venturi section will draw fuel out of the first fuel jet to mix such fuel with the air flowing through the venturi section. This mixture of atomized air flows past the throttle plate, through the intake manifold, and into the cylinders of the engine, where it is ignited and burned in a known manner.
The amount of fuel and air admitted into the engine is regulated primarily by the operation of the throttle plate. As the operator steps upon or otherwise actuates the throttle, the throttle plate pivots to a more fully open position, increasing the amount of air flowing through the venturi section which correspondingly increases the amount of fuel being sucked out of the first fuel jet. Conversely, pivoting the throttle plate to a more closed position will decrease the total air flow and fuel being supplied from the first fuel jet, to thereby decrease the engine speed. This operation of the throttle plate is sufficient to adequately supply the engine with fuel during idling and cruising operations of the engine.
However, at certain times, additional power is required from the engine. For example, sudden acceleration and high speed operation of the engine requires more fuel than the pivotal throttle plate and first fuel jet combination described above can provide. Accordingly, some carburetors of this type are also provided with a second fuel jet located in the carburetor body for admitting additional fuel to the airflow passage to enrich the mixture and cause the engine to provide more power. Peak engine power is often achieved through testing and by adjusting the relative sizes of the first and second fuel jets.
While carburetors can be purchased with all of the required fuel jet assemblies installed by the original equipment manufacturer, carburetors equipped with only a single fuel jet are far more common. In such cases, kits for installing an additional fuel jet can be bought with the second fuel jet being added to the carburetor by the end user in a retrofit manner. However, the procedure for mounting and installing this fuel jet is both cumbersome and time-consuming. In addition, if the installation procedure is not properly done, then the carburetor itself may be damaged or ruined during the installation procedure, perhaps requiring that it be thrown away and a new carburetor purchased.
In installing additional fuel jets in a carburetor, the common practice is to locate a flat area or boss on the side of the carburetor body in the venturi section of the airflow passage. If no such flat area or boss exists on the carburetor body, one may have to be provided using either a milling machine or a file. Then, two holes have to be drilled into this flat area or boss, with the first hole being sized to receive the fuel jet and the second hole being sized to receive an attachment screw that is located on a mounting arm attached to the fuel jet. The first hole is drilled through the entire thickness of the carburetor body to break through into the venturi section with the second hole being drilled only partway and then being tapped or threaded to receive the attachment screw. The fuel jet is then inserted through the first hole and is held in place by the attachment screw which is tightened into the threaded second hole. This procedure is that used for installing a Mikuni Power Jet Kit to a Mikuni carburetor.
This installation procedure requires specialized tools and some experience and skill on the part of an installer. For example, if the hole that receives the additional fuel jet being installed is not drilled properly, it may ruin the entire carburetor, rendering it unfit for further use, or it may position the fuel jet improperly, leading to decreased performance. In addition, the fuel jet is held in place by only a single attachment screw that is received in a tapped hole that has been drilled by the user. Given the extreme vibrations many of these internal combustion engines experience, particularly at idle, such vibrations tend to loosen the fuel jet and cause leakage of fuel from the carburetor. Any such leakage poses an obvious safety risk.